Browsing by Author "Mikkilä, J."
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- ItemEnhancement of atmospheric H2SO4/H2O nucleation: Organic oxidation products versus amines(München : European Geopyhsical Union, 2014) Berndt, T.; Sipilä, M.; Stratmann, F.; Petäjä, T.; Vanhanen, J.; Mikkilä, J.; Patokoski, J.; Taipale, R.; Mauldin III, R.L.; Kulmala, M.Atmospheric H2SO4 / H2O nucleation influencing effects have been studied in the flow tube IfT-LFT (Institute for Tropospheric Research – Laminar Flow Tube) at 293 ± 0.5 K and a pressure of 1 bar using synthetic air as the carrier gas. The presence of a possible background amine concentration in the order of 107–108 molecule cm−3 throughout the experiments has to be taken into account. In a first set of investigations, ozonolysis of olefins (tetramethylethylene, 1-methyl-cyclohexene, α-pinene and limonene) for close to atmospheric concentrations, served as the source of OH radicals and possibly other oxidants initiating H2SO4 formation starting from SO2. The oxidant generation is inevitably associated with the formation of organic oxidation products arising from the parent olefins. These products (first generation mainly) showed no clear effect on the number of nucleated particles within a wide range of experimental conditions for H2SO4 concentrations higher than ~107 molecule cm−3. Also the early growth process of the nucleated particles was not significantly influenced by the organic oxidation products in line with the expected growth by organic products using literature data. An additional, H2SO4-independent process of particle (nano-CN) formation was observed in the case of α-pinene and limonene ozonolysis for H2SO4 concentrations smaller than ~107 molecule cm−3. Furthermore, the findings confirm the appearance of an additional oxidant for SO2 beside OH radicals, very likely stabilized Criegee Intermediates (sCI). A second set of experiments has been performed in the presence of added amines in the concentrations range of a few 107–1010 molecule cm−3 applying photolytic OH radical generation for H2SO4 production without addition of other organics. All amines showed significant nucleation enhancement with increasing efficiency in the order pyridine < aniline < dimethylamine < trimethylamine. This result supports the idea of H2SO4 cluster stabilization by amines due to strong H2SO4↔amine interactions. On the other hand, this study indicates that for organic oxidation products (in presence of the possible amine background as stated) a distinct H2SO4 / H2O nucleation enhancement can be due to increased H2SO4 formation caused by additional organic oxidant production (sCI) rather than by stabilization of H2SO4 clusters due to H2SO4↔organics interactions.
- ItemLaboratory study on new particle formation from the reaction OH + SO2: influence of experimental conditions, H2O vapour, NH3 and the amine tert-butylamine on the overall process(München : European Geopyhsical Union, 2010) Berndt, T.; Stratmann, F.; Sipilä, M.; Vanhanen, J.; Petäjä, T.; Mikkilä, J.; Grüner, A.; Spindler, G.; Lee Mauldin III, R.; Curtius, J.; Kulmala, M.; Heintzenberg, J.Nucleation experiments starting from the reaction of OH radicals with SO2 have been performed in the IfT-LFT flow tube under atmospheric conditions at 293±0.5 K for a relative humidity of 13–61%. The presence of different additives (H2, CO, 1,3,5-trimethylbenzene) for adjusting the OH radical concentration and resulting OH levels in the range (4–300) ×105 molecule cm−3 did not influence the nucleation process itself. The number of detected particles as well as the threshold H2SO4 concentration needed for nucleation was found to be strongly dependent on the counting efficiency of the used counting devices. High-sensitivity particle counters allowed the measurement of freshly nucleated particles with diameters down to about 1.5 nm. A parameterization of the experimental data was developed using power law equations for H2SO4 and H2O vapour. The exponent for H2SO4 from different measurement series was in the range of 1.7–2.1 being in good agreement with those arising from analysis of nucleation events in the atmosphere. For increasing relative humidity, an increase of the particle number was observed. The exponent for H2O vapour was found to be 3.1 representing an upper limit. Addition of 1.2×1011 molecule cm−3 or 1.2×1012 molecule cm−3 of NH3 (range of atmospheric NH3 peak concentrations) revealed that NH3 has a measureable, promoting effect on the nucleation rate under these conditions. The promoting effect was found to be more pronounced for relatively dry conditions, i.e. a rise of the particle number by 1–2 orders of magnitude at RH = 13% and only by a factor of 2–5 at RH = 47% (NH3 addition: 1.2×1012 molecule cm−3). Using the amine tert-butylamine instead of NH3, the enhancing impact of the base for nucleation and particle growth appears to be stronger. Tert-butylamine addition of about 1010 molecule cm−3 at RH = 13% enhances particle formation by about two orders of magnitude, while for NH3 only a small or negligible effect on nucleation in this range of concentration appeared. This suggests that amines can strongly influence atmospheric H2SO4-H2O nucleation and are probably promising candidates for explaining existing discrepancies between theory and observations.